1. Field of the Invention
The present invention is related to an opthalmologic apparatus that includes an ocular fundus tracking controller for detecting a direction of gaze of an examined eye and following an ocular fundus imaging system in the direction of gaze, thereby photographing an ocular fundus with high resolution.
2. Description of the Related Technology
A conventional ocular fundus camera produces a deterioration in an ocular fundus image photographed because of optical aberration owned by the tested eye. Accordingly, the ocular fundus camera has a disadvantage that an clear image of the ocular fundus having high magnification cannot be obtained.
Owing to this, these days, a technology for photographing an ocular fundus image is proposed by which the optical aberration of the tested eye is measured and compensated by using a compensation optical system based on the measured results. The technology can eliminate an influence caused by the optical aberration of the tested eye to produce a higher magnification of the ocular fundus image compared with the conventional technique.
However, the conventional opthalmologic apparatus has difficulties in photographing an ocular fundus image with much higher magnification and higher resolution applied to a visual cell level. One of the difficulties is a fixation micro-movement of an eyeball. That is, the eyeball always continues a micro-movement called a fixation micro-movement, which always moves a gaze direction of the eye. Accordingly, since an ocular fundus image to be photographed is oscillating and causes a blur, it is essential to remove an influence of the fixation micro-movement in order to take a picture of the ocular fundus image with much higher resolution.
So as to get rid of the blur of the ocular fundus image in a difference of the gaze direction of the eye, an opthalmologic apparatus has been proposed in which the gaze direction of the examined eye is detected and tracking is carried out with respect to the ocular fundus based on the detection results. See, for example, U.S. Pat. No. 5,943, 115.
According to the technology disclosed in the US patent, in order to detect a gaze direction of the tested eye on the ocular fundus, a detection beam of a infinitesimal region close to the point light source is projected to the ocular fundus for scanning so that a circular locus is drawn on the ocular fundus. A reflective beam at the ocular fundus of the detection beam is received to detect the gaze direction of the tested eye, which controls a pair of tracking mirror from.
The optical system projects a detection beam on the ocular fundus of the examined eye through the order of a detection light source, a vibration reflective mirror (scanning mirror) for scanning the detection beam in a circular locus on the ocular fundus, a tracking mirror for controlling tracking according to the gaze direction of the examined eye that is detected, and an objective lens. Then, the optical system receives a reflective beam from the ocular fundus via the objective lens, the vibration reflective mirror (scanning mirror) and the tracking mirror.
On the other hand, an area to which a detection beam is projected and at which a reflective beam is detected may be a characteristic portion brighter than the environment, for example, an optic disc. Since a desired region of the ocular fundus other than the characteristic portion should be photographed, projection of the detection beam and shift of the axis of the light receiving system (corresponding to the detection axis of the gaze direction) are arbitrarily adjusted with respect to the optical axis for photographing the ocular fundus.
Because of this, the US patent discloses a structure in which the detection optical axis of the vibration reflection mirror (scanning mirror) to scan the detection beam is shifted by a predetermined amount to shift the detection axis of the gaze direction.
If the technology of the US patent is applied to an opthalmologic apparatus having high magnification, the detection axis of the gaze direction can be shifted in the high magnification observation region. However, when shifting the detection axis of the gaze direction outside the observation region, there is a disadvantage that an effective aperture of the ocular fundus high magnification should be much higher than is necessary. There is a need for a opthalmologic apparatus that can solve the disadvantage.